Conventional mobile devices such as smart-phones typically have a large touchscreen on the front of the device which is covered with glass. A thin metal rear casing concealing the internal components is retained to the glass to form a bezel. For functional reasons however it has been necessary to provide a number of apertures in the glass front, for example in order to allow a sound opening for a coil-based earpiece speaker.
More recently however there has been an increase in the perceived importance of the aesthetics of mobile devices, with physical design becoming a key selling point. This has led some smart-phone manufacturers to remove the conventional coil-based earpiece speaker which requires a sound opening. This helps to achieve an unbroken glass surface on the front of the phone which is considered visually appealing. Removing the earpiece also has the additional benefit that the display can be extended to the top of the bezel leaving only a small strip of area at the bottom of the device-front which does not provide display. Extending the display to the top-bezel allows for a larger display screen for the same phone size.
As a replacement for the coil-based earpiece in such devices, a piezo ceramic actuator is mounted to the main frame in the interior of the device. By driving the piezo actuator, microscopic vibrations spread to the frame and the bezel leading to the generation of audible sound without the use of a dedicated diaphragm. However to extend the display to the top edge of the bezel, other hardware components that normally reside in this area must also be replaced or removed. This applies particularly to the front-camera which needs to be omitted or removed to the lower front part of the phone.
However the approach outlined creates a problem for the proximity sensor which is typically provided. This traditionally comprises an infra-red transmitter and detector. The proximity sensor is typically used to detect when a user puts the phone to their head during a phone conversation, whereupon it sends a signal to deactivate the touchscreen. This prevents accidental inputs to the device (such as deactivating the call) due to contact between the screen and the user's head and also helps to reduce power consumption. The proximity sensor normally needs to be positioned close to the top part of the phone since (i) during a call the top-part is typically closer to the head than the bottom part, and (ii) placement at the bottom could lead to false detections if the user deliberately touched the screen with their hand. This means that the proximity sensor presents a challenge when seeking to achieve a design with the display extending to the top bezel.